Plasma treatment of titanium nitride formed by chemical vapor deposition

ABSTRACT

A method of depositing titanium nitride by chemical vapor deposition in a chamber having several design features directed to the conductive nature of titanium nitride, particularly when a plasma treatment step is performed after the thermal deposition of the film. Preferably, during the post-deposition plasma treatment, RF power is applied only to the showerhead counter-electrode and none to the pedestal supporting the wafer, thereby preventing charging of the wafer.

RELATED APPLICATION

This application is a divisional of Ser. No. 08/680,724, filed Jul. 12,1996, now issued as U.S. Pat. No. 5,846,332.

FIELD OF THE INVENTION

This invention relates to semiconductor fabrication equipment. Inparticular, the invention relates to components used in a plasma reactorfor chemical vapor deposition (CVD) pertaining to gas flow through andout of the reactor chamber.

BACKGROUND OF THE INVENTION

Semiconductor integrated circuits are fabricated with multiple layers,some of them patterned, of semiconductive, insulating, and conductivematerials, as well as additional layers providing functions such asbonding, a migration barrier, and an ohmic contact. Thin films of thesevarious materials are deposited or formed in a number of ways, the mostimportant of which in modem processing are physical vapor deposition(PVD), also known as sputtering, and chemical vapor deposition (CVD).

In CVD, a substrate, for example, a silicon wafer, which may alreadyhave patterned layers of silicon or other materials formed thereon, isexposed to a precursor gas which reacts at the surface of the substrateand deposits a product of the reaction on the substrate to thereby growa film thereon. A simple example includes the use of silane (SiH₄) todeposit silicon with the hydrogen forming a gaseous byproduct which isevacuated from the chamber. However, the present application is directedmore to CVD of a conductive material such as TiN.

This surface reaction can be activated in at least two different ways.In a thermal process, the substrate is heated to a sufficiently hightemperature to provide the activation energy for molecules of theprecursor gas adjacent to the substrate to react there and deposit alayer upon the substrate. In a plasma-enhanced CVD process (PECVD), theprecursor gas is subjected to a sufficiently high field that it forms aplasma. As a result the precursor gas is excited into higher energeticstates, such as ions or radicals, which readily react on the substratesurface to form the desired layered material.

Zhao et al. describe an example of a CVD deposition chamber in U.S.patent application Ser. No. 08/348,273 filed on Nov. 30, 1994, nowissued as U.S. Pat. No. 5,558,717, expressly incorporated herein byreference, and which is assigned to a common assignee. This type of CVDchamber is available from Applied Materials, Inc. of Santa Clara, Calif.as the CVD DxZ chamber.

As described in this patent and as illustrated in the cross sectionalside view of FIG. 1, a CVD reactor chamber 30 includes a pedestal 32supporting on a supporting surface 34 a wafer 36 to be deposited by CVDwith a layer of material. Lift pins 38 are slidable within the pedestal32 but are kept from falling out by conical heads on their upper ends.The lower ends of the lift pins 38 are engageable with a verticallymovable lifting ring 39 and thus can be lifted above the pedestal'ssurface 34. The pedestal 32 is also vertically movable, and incooperation with the lift pins 38 and the lifting ring 39, anunillustrated robot blade transfers a wafer into chamber 30, the liftpins 38 raise the wafer 36 off the robot blade, and then the pedestalrises to raise the wafer 36 off the lift pins 38 onto its supportingsurface 34.

The pedestal 32 then further raises the wafer 36 into close oppositionto a gas distribution faceplate 40, often referred to as a showerhead,which includes a large number of passageways 42 for jetting the processgas to the opposed wafer 36. That is, the passageways 42 guide theprocess gas into a processing space 56 towards the wafer 36. The processgas is injected into the reactor 30 through a central gas inlet 44 in agas-feed cover plate 46 to a first disk-shaped manifold 48 and fromthence through passageways 50 in a baffle plate 52 to a seconddisk-shaped manifold 54 in back of the showerhead 40.

As indicated by the arrows, the process gas jets from the holes 42 inthe showerhead 40 into the processing space 56 between the showerhead 40and pedestal 32 so as to react at the surface of the closely spacedwafer 36. Unreacted process gas and reaction byproducts flow radiallyoutwardly to an annular pumping channel 60 surrounding the upperperiphery of the pedestal 32. The pumping channel 60 is generally closedbut on the receiving end includes an annular choke aperture 62 betweenthe pumping channel 60 and the processing space 56 over the wafer 36.The choke aperture 62 is formed between an isolator 64, to be describedlater, set in a lid rim 66 and an insulating annular chamber insert 68resting on a ledge 70 on the inside of the main chamber body 72. Thechoke aperture 62 is formed between the main chamber and a removable lidattached to the chamber so that a fully annular choke aperture 62 can beachieved. The choke aperture 62 has a substantially smaller width thanthe depth of the processing space 56 between the showerhead 40 and thewafer 36 and is substantially smaller than the minimum lateraldimensions of the circumferential pumping channel 60, for example by atleast a factor of five. The width of the choke aperture 62 is made smallenough and its length long enough so as to create sufficient aerodynamicresistance at the operating pressure and gas flow so that the pressuredrop across the choke aperture 62 is substantially larger than anypressure drops across the radius of the wafer 36 or around thecircumference of the annular pumping channel 60. In practice, it is notuntypical that the choke aperture 62 introduces enough aerodynamicimpedance that the pressure drop from the middle of the wafer 36 towithin the pumping channel 60 is no more than 10% of the circumferentialpressure drop within the pumping channel 60.

The pumping channel 60 is connected through a constricted exhaustaperture 74 to a pumping plenum 76, and a valve 78 gates the exhaustthrough an exhaust vent 80 to a vacuum pump 82. The constricted exhaustaperture 74 performs a function similar to that of the choke aperture 62in introducing an aerodynamic impedance such that the pressure withinthe pump channel 60 is substantially constant.

The restricted choke and exhaust apertures 62, 74 create a nearlyuniform pressure around the circumferential pumping channel 60. Theresultant gas distribution flow pattern across the wafer 36 is shown inarrowed lines 84 in FIG. 2. The process gas and its reaction byproductsflow from the center of the showerhead 40 across the wafer 36 and theperiphery of the pedestal 32 along radial paths 84 and then through thechoke aperture 62 to the pumping channel 60. The gas then flowscircumferentially along paths 86 in the pumping channel 60 to theexhaust aperture 74 and then through the exhaust plenum 76 and theexhaust vent 80 to the vacuum pump 82. Because of the restrictions 62,74, the radial flow 84 across the wafer 36 is nearly uniform in theazimuthal direction.

As shown in FIGS. 1 and 3 (FIG. 3 being a closeup view of the upperright corner of FIG. 1), the ledge 70 in the chamber body 72 supportsthe chamber shield liner 68, which forms the bottom of the pumpingchannel 60. The chamber lid rim 66 forms the top and part of the outsidewall of the pumping channel 60 along with part of the chamber body 72.The inside upper edge of the pumping channel 60 is formed by theisolator ring 64, which is made of a ceramic or other electricallyinsulating material which insulates the metallic showerhead 40 from thechamber body 72.

The CVD reactor 30 of FIG. 1 can be operated in two modes, thermal andplasma-enhanced. In the thermal mode, an electrical power source 90supplies power to a resistive heater 92 at the top of the pedestal 32 tothereby heat the pedestal 32 and thus the wafer 36 to an elevatedtemperature sufficient to thermally activate the CVD depositionreaction. In the plasma-enhanced mode, an RF electrical source 94 ispassed by a switch 96 to the metallic showerhead 40, which thus acts asan electrode. The showerhead 40 is electrically insulated from the lidrim 66 and the main chamber body 72 by the annular isolator ring 64,typically formed of an electrically non-conductive ceramic. The pedestal32 is connected to a biasing element 98 associated with the RF source 94so that RF power is split between the showerhead 40 and the pedestal 32.Sufficient voltage and power is applied by the RF source 94 to cause theprocess gas in the processing region 56 between the showerhead 40 andthe pedestal 32 to discharge and to form a plasma.

Only recently has it been attempted to use this general type of CVDreactor to deposit a film of a conductive material, such as titaniumnitride (TiN), using the thermal TDMAT process described by Sandhu etal. in U.S. patent application, Ser. No. 07/898,059. A related plasmaprocess is described by Sandhu et al. in U.S. Pat. No. 5,246,881. Thedeposition of a conductive material in this chamber has presented someproblems that are addressed by this invention.

Titanium nitride is a moderately good electrical conductor, but insemiconductor processing it is used primarily to function as a barrierlayer and to assist titanium as a glue layer. This process is oftenapplied to the contact structure illustrated in the cross-sectional viewof FIG. 4 in which an oxide layer 100, typically SiO₂, is deposited to athickness of about 1 μm over a substrate 102 having a surface ofcrystalline silicon or polysilicon. The oxide layer 100 acts as aninter-level dielectric, but to provide electrical contact between levelsa contact hole 104 is etched through the oxide layer 100 to be filledwith a metal such as aluminum. However, in advanced integrated circuits,the contact hole 104 is narrow, often less than 0.35 μm, and has anaspect ratio of 3 or more. Filling such a hole is difficult, but asomewhat standard process has been developed in which the hole 104 isfirst conformally coated with a titanium layer 106, and the titaniumlayer 106 is then conformally coated with a titanium nitride layer 108.Thereafter, an aluminum layer 110 is deposited, usually by physicalvapor deposition, to fill the contact hole 104 and to provide electricalinterconnection lines on the upper level. The Ti layer 104 provides aglue layer to both the underlying silicon and the oxide on thesidewalls. Also, it can be silicided with the underlying silicon to forman ohmic contact. The TiN layer 106 bonds well to the Ti layer 104, andthe aluminum layer 110 wets well to the TiN so that the aluminum canbetter fill the contact hole 104 without forming an included void. Also,the TiN layer 106 acts as a barrier to prevent the aluminum 110 frommigrating into the silicon 102 and affecting its conductivity. In a viastructure in which the substrate 102 includes an aluminum surfacefeature, the Ti layer 104 may not be needed. Even though the electricalconductivities of titanium and titanium nitride are not nearly as highas that of aluminum, they are sufficiently conductive in thin layers toprovide a good electrical contact.

Titanium and titanium nitride can be deposited by either CVD or PVD, butCVD enjoys the advantage of more easily forming conformal layers in ahole having a high aspect ratio. The thermal TDMAT process is such a CVDprocess for conformally coating TiN in a narrow hole.

In the TDMAT process, a precursor gas oftetrakis-dimethylamido-titanium, Ti(N(CH₄)₂)₄, is injected into thechamber through the showerhead 40 at a pressure of about 1 to 9 Torrwhile the pedestal 32 holds the substrate 36 at an elevated temperatureof about 360° C. or higher. Thereby, a conductive and conformal TiNlayer is deposited on the substrate 36 in a CVD process. The TDMATprocess is a thermal process not usually relying upon plasma excitationof the precursor gas.

However, it has been found that the TiN layer initially formed by theTDMAT process includes an excessive amount of carbon in the form ofincluded polymers which degrade its conductivity. Thus, the TDMATdeposition is usually followed by a second step of plasma treating thedeposited TiN layer. The TDMAT gas in the chamber is replaced by an gasmixture of H₂ and N₂ in about a 50:50 ratio at a pressure of 0.5 to 10Torr, and the RF power source 94 is switched on to create electricfields between the showerhead 40 and the pedestal 32 sufficient todischarge the H₂:N₂ gas to form a plasma. The hydrogen and nitrogenspecies in the plasma reduce the carbonaceous polymer to volatilebyproducts which are exhausted from the system. The plasma treatmentthereby removes the carbon to improve the quality of the TiN film.

The plasma treatment process, when performed in the same chamber as thethermal CVD deposition, has demonstrated some problems with uniformityand reproducibility. We believe that the problems originate fromextraneous metal depositions on reactor surfaces affecting the plasmaand producing excess particles within the chamber. We also believe thatthe depositions occur in two different areas, an area at the top of thepedestal 32 outside of the substrate 36 and an area in and around thepumping channel 60.

A first problem, we believe, relates to extraneous metal deposition onthe pedestal 32 because exposed portions of the pedestal 32 are at atemperature equal to and often much greater than that of the wafer 36.As shown in the cross-sectional view of FIG. 3, the portion of thepedestal 32 which extends beyond the outside edge of the wafer 36 issubject to a buildup 120 of deposited material from the followingmechanism.

During the thermal phase of the TDMAT process during which theconductive TiN is deposited, the heater 92, shown in FIG. 1, installedin the pedestal 32 heats the pedestal 32, and the heat is transferredthence to the wafer 36. There are several reasons why the exposedportion of the pedestal 32 tends to be at a significantly highertemperature than that of the wafer 36. The showerhead 40 operates at amuch lower temperature, typically around 100° C. to readily sink heatfrom opposed elements. On the other hand, the wafer 36 is incompletelyheat sunk on the pedestal 32 and transmits heat conducted to it from thepedestal 32 more poorly than does the directly radiating and more highlythermally conductive pedestal 32. Also, since the chamber is also usedfor the low-temperature plasma treating phase and additional time isconsumed transferring wafers into and out of the chamber, the duty cyclefor the high-temperature operation is relatively low and it is necessaryto heat the wafer 36 to the required high processing temperatures. Toquickly raise the temperature of the wafer 36 to its processingtemperature, the temperature of the pedestal 32 is raised to a highertemperature than that of the wafer 36. For all these reasons, theprocessing temperature of the wafer 36 may be set to 360° C. while theexposed portion of the pedestal tends to be at a significantly highertemperature of 425° C.

Since the rate of deposition on a surface is proportional to thetemperature of the surface (the higher the temperature the more rapidthe deposition), the higher temperature of the exposed outer edge of thepedestal 32 causes, as illustrated in FIG. 3, a rapid buildup 120 ofdeposited film. As the thickness of the deposited film increases overthe processing cycles of many wafers, deleterious effects may occur. Thebuild up of film thickness at the edge may create an artificialperimeter rim which prevents the wafer 36 from being in full contactwith the surface of the pedestal 32, as required for efficientprocessing. Similarly, once the build up 120 has developed past somefilm thickness of the film, successively deposited film layers do notcompletely adhere to the underlying layers. Portions of the film canthen form particles or flakes that separate from the pedestal and floatonto the wafer 36 being processed. The particles can create defects onthe processed wafer.

A second problem related to extraneous metal deposition arises in thatthe conductive TiN film is also deposited, to a lesser extent because oflower surface temperatures, on other surfaces exposed to the process gasalong its path from the showerhead 40 to and through the pumping channel60 on its way to the chamber vacuum system 82. FIG. 5 shows an exampleof the buildup of a metal film 124 over and around the isolator ring 64that can cause an electrical short between the electrically biasedshowerhead 40 and the grounded lid rim 66. FIG. 5 shows only anexaggerated film buildup 124 on the upper surface of the chamber. Inreality, the film builds up on all surfaces, but the other buildup isnot shown for clarity.

Another example of extraneous film deposition illustrated in FIG. 6 isthe buildup of a conductive film 128 over the insulating alumina chamberinsert 68 to the point that it extends across the pumping channel 60 andcontacts the electrically grounded main chamber body 72. This extraneousdeposition 128 thus extends the ground potential associated with thechamber body 72 and the lid rim 66 to the inner, upper edge of theinsulating annular insert 68 closely adjacent the upper peripheral edgeof the pedestal 32. The location and quality of plasma in the processingspace 56 depends on the distance between the powered plasma sourceelectrodes and surrounding surfaces and the difference between theirrespective electrical potentials. When, during a long process run, thechamber insert 68 effectively changes from being disposed as a insulatorbetween the chamber body 68 and the plasma to being a groundedconductor, the location and quality of the plasma will be affected,particularly around the edges of the substrate 36. The distortion of theplasma due to the proximity of a closely adjacent electrical groundcauses non-uniformity in the plasma, which affects the thickness of thefilm deposition and its surface properties.

During plasma processing, variations in uniformity of the plasma willaffect the surface uniformity of the film produced. Therefore,variations in the intensity of the plasma will affect the uniformity offilm properties. The conductivity, which is the inverse of theinsulating quality, of the insulating members surrounding the locationof the plasma changes as a conductive film is formed on their surfacesand as the conductive film forms a conductive path to adjacentconductive elements at different potentials. This variation in theconductive quality of the ostensibly insulating elements causesvariations in the plasma which reduce the process repeatability.

A third problem related to extraneous metal deposition arises in thatsome electrically floating elements which are exposed to the plasma willaccumulate a charge from the plasma. In the instance where these chargedpieces are close to a grounded or electrically powered part, there isalways a chance of arcing between the floating part and a ground or theelectrode. In the instance when the wafer is supported on the pedestal,the wafer may act as a floating element which can become charged tocause arcing. Arcing creates particles and defects in the substrate.Therefore arcing to the wafer should be avoided and the uniformity ofthe envelope for the plasma treating the surface of the substrate shouldbe held as uniform as possible.

To avoid these potentially deleterious effects, it is common practice toschedule a cleaning or maintenance cycle involving removal andreplacement or cleaning of the pedestal before buildup of film cancreate undesired effects. However, this remedy is disadvantageous. Notonly are pedestals expensive, but their replacement or cleaning involvesa shut down of expensive equipment and additional operator time.

The buildup of unwanted film thickness on either the perimeter of thesusceptor or across insulating members in the chamber requires they beperiodically cleaned to prevent short circuiting or unacceptablevariations in the plasma treatment. The buildup of a thickness of anunwanted film creates a risk of short circuiting by causing variationsin the intensity and location of the electrical fields exciting the gasto a plasma state. Also, when the risk of conduction or arcing becomeshigh, a cleaning or maintenance cycle is initiated to restore theoriginal distribution of the electrical field. Other consumable ormaintainable components also require replacement or cleaning at certainintervals. Presently the risk of conductance and arcing sets thecleaning/maintenance interval. The mean number of wafers between cleanscould be increased dramatically if the problem of film thicknessadherence and conductivity across insulating members to groundedmembers, as described above, could be reduced or eliminated.

A CVD chamber, schematically illustrated in FIG. 7, is similar to thatof FIG. 1 except that is radiantly, not resistively, heated. It has beenapplied to the deposition of conductive materials and where plasmatreatment of one sort or another was performed in the chamber. In thischamber, an argon treatment sputtering gas was energized into a plasma130 between a pedestal electrode 132 and a counter electrode 134. An RFpower source 136 provides RF power to energize the plasma. It was found,however, that, if the plasma was to be well confined in the processingspace above the wafer, it was necessary to feed the RF power to amatching network 138 that selectably split the power between thepedestal electrode 132 and the counter electrode 134. It is believedthat thus splitting the RF power better confines the plasma because theplasma with a grounded electrode tends to spread outside of the area ofthe wafer and to be more affected by the extraneously deposited metallayers described above. The matching network 138 allowed the RF powersplit to the pedestal electrode 132 to be the fraction of 30%, 50%, or70% of the total power.

It is desired that CVD chambers of the type shown in FIG. 1, which weredesigned for deposition of dielectrics, be adapted to allow them todeposit metallic materials.

Therefore, it is desired that this chamber be improved to alleviate theproblems of plasma instability and arcing. It is further desired thatthe frequency for routine maintenance and cleaning be reduced.

SUMMARY OF THE INVENTION

This invention extends the mean number of wafers between cleans byimproving the performance of a semiconductor substrate processingchamber, for example, a chamber for depositing titanium nitride.

The performance is improved by reducing the tendency of the depositiongas to form an excessive build up on the portion of the susceptorextending beyond the edge of the substrate being processed. Reducing thetemperature of a peripheral ring surrounding the outer edge of thesubstrate being processed reduces the build up.

The invention includes a peripheral ring on the substrate supportpedestal which is thermally isolated from the pedestal and the substratebeing processed. The peripheral ring includes centering bosses extendingabove the ring which assist in centering the substrate as it is loweredto the surface of the support pedestal. The centering bosses provide aseries of protruding features extending inward from the inside perimeteredge of the ring facing the substrate. These protrusions potentially arethe only part of the peripheral ring in contact with the substrate,thereby providing a minimum of surface contact (and potential forconductive heat transfer) between the substrate and the peripheralcentering ring.

The peripheral centering ring is thermally isolated from the pedestal bybeing supported on pins at only three locations around the peripherythereby reducing the conductive heat transfer from the pedestal to theperipheral centering ring. The thermal isolation from the pedestal isfurther achieved by providing a series of isolator rings or radiationshields (for example, two) which are attached to the bottom side of theperipheral ring. The radiation shields act as barriers to prevent thedirect transmission of thermal radiation from the pedestal to theperipheral centering ring. The lower temperature of the peripheral ringas a result of this thermal isolation causes a lower rate of vapor filmdeposition on its surface and increases the mean number of wafersbetween cleaning cycles for the processing chamber. The separateperipheral ring can easily be removed and replaced during a maintenancecycle of the processing chamber.

The peripheral ring being thermally isolated from the pedestal issubject to a build up of static charge which can result in arcing to andfrom the wafer and/or other adjacent surfaces. The invention includes agrounding strap between the peripheral ring and the pedestal toeliminate arcing between the peripheral ring and the substrate or otheradjacent surfaces. The ground strap is flexible and is mounted in arecessed slot on the perimeter of the susceptor such that the groundstrap does not provide a protrusion which extends beyond the normalnominal perimeter of the susceptor.

Performance is also improved by reducing and nearly eliminating thelikelihood that a continuous conductive film will be formed acrossinsulating elements within the chamber. A continuous choke gap iscreated in and between adjacent elements having different electricalpotentials across which a conductive film might create a change ininsulating properties.

An isolating member (ring) in the lid of the processing chamber,includes a series of continuous choke gap surface features (grooves)which prevent the formation of continuous conductive film on the surfaceof the isolation member. The film formed on the surface is notcontinuous and therefore does not provide a conductive path from the gasdistribution faceplate/electrode to ground. Electrical or chargeconduction and/or leakage to ground will eliminate or reduce theelectrical field needed to form a uniform plasma and to provide uniformprocessing of substrates through consecutive processing cycles.

To reduce the possibility of grounding of the metal shield surroundingthe plasma region, a (second) continuous choke gap is created around theprocessing chamber between a second shield element and the chamber body.While still susceptible to having conductive films being formed therein,the width and depth of the gap prevents the surface film from forming aconductive bridge or connection across the gap or within the gap.

Performance is further improved by providing an electrically floatingconductive element surrounding the plasma location to stabilize the edgeof the plasma envelope. In one instance a metal shield, which iselectrically floating, lines a portion of a wall of the substrateprocessing chamber. The shield becomes coated during vapor deposition,but process stability is maintained because the shield is electricallyisolated from surrounding conductive elements. The shield provides abarrier to passage of the plasma. The static charge on the conductive(metal) shield is uniformly distributed across it and as a result theedge of the plasma envelope is stabilized.

Another improvement involves using RF power provided exclusively to theupper electrode (the gas distribution plate) while the lower electrode(susceptor) is grounded. This 100% to 0% power splitting proves animprovement in the uniform properties of film in a chamber performing aTiN film deposition.

The invention includes a method of isolating a peripheral ring in asusceptor extending beyond the edge of the substrate, including steps ofproviding a series of support point features from the top of thesusceptor and providing a radiation shield ring shielding a portion ofthe peripheral ring from direct exposure to the susceptor. Anothermethod includes the steps of providing a grounding strap that iselectrically connected to the peripheral ring and removably attaching aportion of the grounding strap to the susceptor. Another method of theinvention includes the steps of providing an isolator ring exposed atleast on one side to the atmosphere of the processing chamber between anRF powered electrode and an electrically conductive element having anelectrical potential different from the RF powered electrode, andproviding a continuous choke gap in the surface of the isolator memberfacing the atmosphere of the processing chamber. Another feature of theinvention includes a method including the steps of providing a shieldsupported by an insulating member within the process chamber andproviding a clearance between the inner shield member and a groundedsurface such that a film forming on the surface will not bridge the gapto provide conductivity.

The invention also includes a method of providing power to a TiN vapordeposition chamber including the steps of connecting an electrode gasdistribution plate to a power source and connecting a susceptor oppositethe electrode gas distribution plate to the electrode to a groundpotential.

This invention provides improvements which reduce the chance of arcingbetween floating charged elements in the processing chamber adjacent tothe location where plasma is formed, reduce the temperature of theperipheral ring to avoid excessive deposition on the part of thesusceptor outside the substrate, provides a constant potential acrossthe substrate to eliminate arcing between its peripheral/centering ringand the susceptor and eliminates or substantially reduces the likelihoodthat any film formed by the vapor deposition on the chamber walls willresult in a short circuit connection between the RF electrode and achamber body or lid. The invention also includes the positioning of ametal (uniform electrical potential distribution ring) around the regionof the plasma to contain the plasma and help keep it stable with arelatively constant ion potential across the wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a prior-art CVD processing chamber.

FIG. 2 is a cross-sectional view of FIG. 1 taken at 2—2 showing the gasflow distribution across the substrate being processed and the gas flowin the pumping channel.

FIG. 3 is an schematical closeup view of the upper right hand corner ofthe chamber as shown in FIG. 1.

FIG. 4 is a cross-sectional view of an integrated-circuit structurewhich the apparatus of the invention can be used to make.

FIG. 5 is a copy of FIG. 3 showing a conductive film formed on the uppersurfaces of the chamber.

FIG. 6 is a copy of FIG. 3 showing a film deposited on the pumpingchannel protruding into the area exposed to plasma in the chambers.

FIG. 7 shows the power splitting energization for prior art TiNchambers.

FIG. 8 is a cross-sectional of a processing chamber according to theinvention.

FIG. 9 is a schematical cross section of the processing chamber of FIG.8 showing the interrelationship between the electrical potentials of thestructures according to the invention and emphasizing other features.

FIG. 10 is an enlarged view of the upper right hand corner of FIGS. 8and 9.

FIG. 11 is a perspective cutaway view of the cross section of FIG. 8showing the interrelationship of various structures of the invention.

FIG. 12 copies FIG. 10 and shows the build up of a conductive filmaround a pumping channel liner of the invention.

FIG. 13 copies FIG. 10 and shows the build up of a conductive film onthe novel isolator ring of the invention as would occur from gastraveling from the gas distribution faceplate to the vacuum evacuationsystem through the pumping channel.

FIG. 14 is a top view of a circular substrate located in a centeringring of a susceptor according to the invention.

FIG. 15 shows a partially sectioned perspective view of a centering bossas part of the centering ring according to the invention.

FIG. 16 shows a closeup plan view of a section of the centering ringwith a substrate in position taken at the closeup identified as 16—16 inFIG. 14.

FIG. 17 is similar to FIG. 15 but shows a wafer which has been centeredby the boss on the centering ring.

FIG. 18 is a partially sectioned perspective view showing the centeringring, its pin support, and its thermally insulating rings taken at 18—18in FIG. 14.

FIG. 19 a partially sectioned perspective view of the centering ring(without the substrate present) showing the fastener for the thermallyinsulating rings taken at 19—19 of FIG. 14.

FIG. 20 is a partially sectioned exploded perspective view of FIG. 14taken at 20—20 showing the grounding strap of the centering ring withthe centering ring shown separated from the pedestal.

FIG. 21 shows a schematic diagram of an RF power supply to generateplasma in the processing chamber according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 8 shows a cross section of a processing chamber according to afirst aspect of the invention. A pedestal 140 supports a wafer 142 onits upper surface 144. Gas entering the process gas inlet 44 isdistributed in the lower manifold 54 and passes into the processingregion 56 of the chamber through the nozzles 42 in the showerhead 40.The process gas then flows as shown in FIG. 2 radially outwardly acrossthe edge of the wafer 142, across a peripheral centering ring 146, shownin FIG. 8, disposed in an annular ledge 148 recessed in the upperperiphery of the pedestal 140. From thence, the process gas flowsthrough a choke aperture 150 formed between the bottom of a modifiedannular isolator 152 and the top of a modified chamber wall insert 154and into a modified pumping channel 160. The chamber wall insert 154 isshown to have a sealable passageway 156 through it and through the mainchamber body 72 for an unillustrated robot blade to transfer wafers intoand out of the reactor.

The gas, once it enters the pumping channel 160, is routed around theperimeter of the process chamber, similarly to the prior-art pumpingchannel 60 as shown in FIGS. 1 and 2, to be evacuated by the vacuumpumping system 82 connected to the process chamber.

The same general chamber is illustrated in FIG. 9 with different aspectsof the invention being emphasized. The blown up cross section of FIG. 10includes inventive aspects of both FIGS. 8 and 9.

The generally illustrated chamber insert 154 includes an L-shapedinsulating ceramic ring 164 resting on the inside ledge 70 of the mainchamber body 72 and also includes an annular or band shield 166 restingon an inside ledge 168 of the L-shaped ring 164 and spaced from thepedestal 140 and the centering ring 146 by a small gap. Ceramic chamberliners of themselves are well known, for example, as described byRobertson et al. in U.S. Pat. No. 5,366,585. The band shield 166 ispreferably made of a metal, such as aluminum, and extends verticallyupwardly substantially above the top of the L-shaped ceramic ring 164and to a lesser extent above the supporting surface 144 of the pedestal140.

The annular pumping channel 160 has sides generally defined by the bandshield 166, the L-shaped ring 164, liners 170, 172 placed in front ofthe main chamber body 72 and the lid rim 66, and the isolator 152, withthe choke aperture 150 being formed between the isolator 152 and theband shield 166. However, the lid liner 170 is placed on the side of thepumping channel 160 facing the lid rim 66 and conforms to its shape. Thechamber liner 172 is placed on the side of the pumping channel 160facing the main chamber body 72. Both liners 170, 172 are preferablymade of a metal, such as aluminum, and are bead blasted to increase theadhesion of any film deposited thereon. The lid liner 170 is detachablyfixed to the lid rim 66 by a number of pins 174 and is electricallygrounded to the lid rim 66. However, the chamber liner 172 is supportedon a ledge 176 formed on the outer top of the L-shaped ceramic ring 164and is precisely formed to have a diameter such that a radial gap 178 isformed between the chamber liner 172 and the main chamber body 72, andan axial gap 180 is formed between the lid and chamber liners 170, 172.That is, the chamber liner 172 is electrically floating.

The band shield 166 and the lid and chamber liners 170, 172 are sized asa set. The band shield 166 is annular having a major diameter d₁ aboutthe center of pedestal 140. The chamber liner 172 is also annular and inthe shape of a band extending axially along the centerline of thepedestal 140 and with a major diameter d₂ greater than d₁. The lid liner170 is also annular and has an L-shape with the long, leg extendingradially from d₁ to d₂ and a short leg extending axially at d₂.

A partially sectioned, perspective view is given in FIG. 11 of thepedestal 140, centering ring 146, and the liners 170, 172 and shields152, 166 surrounding the pumping channel 160. This figure clearly showsthe flow of processing gas out of the nozzles 42 of the showerhead 40towards the wafer 142 and the subsequent radially outward flow 84 overthe wafer 142 and then the centering ring 146. Thereafter, the gas flowsis deflected upwardly over the top of the band shield 166 into thepumping channel 160, and in the pumping channel 160 it flows along acircumferential path 86 towards the vacuum pump.

The discussion of the pumping channel will be completed before thecentering ring is again discussed.

As most clearly shown in FIG. 10, the pumping channel 160 and itscomponents are designed to minimize the effect of any depositedconductive film upon the excitation of a plasma in and near theprocessing space 56.

Since the band shield 166 rises above the level of the wafer 142 and ofmost of the gas flowing over it, a dead space 184 is created in the flowpattern at the bottom of the pumping channel 160 adjacent to a top 186of the L-shaped ring 164 where it meets the band shield 166. As aresult, even though metal may deposit on the upper portion of the bandshield 166, the dead space 184 ensures that a significant thickness ofmetal will not deposit around the backside of the band shield 166, andin particular an insufficient amount of metal will deposit to bridge agap 188 formed between the band shield 166 and the top 186 of theL-shaped insulating ring 164. As a result, the band shield 166, eventhough conducting, remains electrically floating with respect to thepedestal 140 and the main chamber body 72. The band shield 166 hasrounded ends 167 to reduce the possibility of arcing.

As is shown in FIG. 12, it is possible for the process gas to flow alonga path 190 in the pumping channel 160 through the axial gap 180 at thetop of the chamber liner 172 and then deposit a conductive film 192 inthe axial gap 180 and in the radial gap 178 on the backside of thechamber liner 172. Since both gaps 178, 180 are dead space, it isunlikely that enough thickness would deposit to bridge either gap 178,180, and, even if it would, any short across the gap would only groundthe chamber liner 172. Another extraneous film in the pumping channel160 would be required to bring the ground from the main chamber body 72close enough to the processing space 56 to significantly affect theplasma fields. Very little, if any, gas will progress down to the bottomend of the radial gap 178 where deposition, if it occurs, might create abridge between the chamber liner 172 and the main chamber body 72.However, because the chamber liner 172 is mounted on an outside ledge176 of the insulating L-shaped ring 164, a conductive film would have tofill the gap between the L-shaped ring 164 and the main the chamber body72 for the ground of the main chamber body 72 to extend to the bandshield 90.

As shown in FIG. 13, an extraneous conductive film 120 deposited on theinsulating ceramic isolator 152 on surfaces in and near the pumpingchannel 160 has the potential of extending the grounding plane of thelid rim 66 to the area adjacent to the biased showerhead 140 tosignificantly perturb the plasma electric fields and perhaps even toshort the biased showerhead 140 across the isolator 152 to the chamberlid rim 66. However, as shown more clearly in FIG. 10, the L-shapedisolator 152 is formed on the outer side of the lower part of itsdepending inner skirt 203 with two deep annular grooves 205, 207 havingwidths sufficient to ensure that the deposited film 120 will not bridgethe grooves 205, 207. Also, the grooves 205, 207 are deep enough that adead space occurs at their bottom so that, even though some depositionis inevitable, it does not form a continuous film on the interiorsurfaces of the grooves 205, 207. In addition, the openings of thegrooves 205, 207 into the pumping channel 190 are generally rounded toprevent arcing from any built up conductive film. As exemplarydimensions, the grooves 205, 207 may have a width of 40 to 80 mils (1-2mm) and a depth of 100 to 175 mils (2.5-4.6 mm) in the case that theisolator 152 has a width in the skirt 203 of 200 to 400 mils (5-10 mm).With this structure, even if the extraneous film 120, as illustrated inFIG. 13, does deposit on the isolator 152, it does not form a continuousconductive film. Thereby, neither is the showerhead 140 shorted out noris an extraneous grounding plane established adjacent to the showerhead140.

The lid liner 170, as illustrated in FIG. 10, is metallic and is boththermally and electrically connected to the lid rim 66, effectivelyforming an extension of it, and because of its remote location does noteasily affect the plasma in the processing region 56. Any metaldepositing on the lid liner 170 will not further affect the plasma aslong as the metal does not extend over the isolator ring 152. In anycase, the lid liner 170 is easily removed by means of the fastener 174when it becomes excessively coated.

The discussion will now turn to the centering ring.

The centering ring 146 performs two functions. It acts to preciselycenter the wafer 142 on the pedestal 140, the wafer 142 having beentransferred into the chamber and onto the pedestal 140 by a robot blademoving through the access passageway 156 of FIG. 8. This function blendswith a retaining finction in which the peripheral ring 146 acts as aretaining ring to hold the wafer 142 within its opening. Additionally,the centering ring 146 acts as a thermal blanket for the portion of thepedestal 140 exposed outside of the wafer 142. Specifically, its thermalcharacteristics are designed in view of the intended process so that thecentering ring 146 thermally floats relative to the heated pedestal 140and remains relatively cool compared to the wafer 142 and significantlycooler than the underlying pedestal 140, and thus little material isdeposited on it during thermal CVD processing.

The centering function and the structure used to achieve it will beexplained first.

The centering ring 146, as illustrated in plan view in FIG. 14 and in asectioned perspective view in FIG. 15, includes an flat annular uppersurface 190 and inside and below this surface 190 an annular ledge 192,which is sized so as to closely face the wafer 142 with a thin gapbetween it and the wafer 142 so as to provide thermal insulation but tononetheless create a barrier to gas flow. The wafer 142 shown in FIG. 14is substantially circular, as is the centering ring 146. However, if thewafer is formed with a large alignment flat on one edge, the inside ofthe centering ring 146 should be shaped to conform to the flat. As shownin FIG. 15, a step wall 194 rises from the ledge 192 to the flat uppersurface 190 of the centering ring 146. The height of the step wall 194equals or is somewhat more than the thickness of the wafer 142 so thatthe top surface of the wafer 142 supported on or cantilevered slightlyabove the surface of the ledge 192 is even with the upper surface 190 ofthe centering ring.

A series of six centering bosses 200, also shown in expanded plan viewof FIG. 16, are equally distributed at 60° intervals about the centeringring 146 with respect to a center 201 of the pedestal 140 to which thecentering ring 146 is also concentric. The centering bosses 200 risefrom the ledge 192 but only partially protrude radially inwardly fromthe step wall 194. The bosses include a cylindrical base 202 and atruncated cone 204 above it, the separation line 203 being somewhatbelow the planar upper surface 190 of the centering ring so that thetruncated cone 204 projects above the planar upper surface 190. Eventhough the centering boss is defined in these simple geometric terms,both the convex and concave corners of the boss 200 are smoothed toreduce any arcing or chipping of the wafer. Related centering pinsthough mounted in the pedestal have been disclosed by Lei et al. in U.S.Pat. No. 5,516,367.

The centering ring 146 is supported on the pedestal 140 by mechanicalmeans to be described later. When the robot blade transfers a wafer 142into the chamber, both the pedestal 140 and the lift ring 39 of FIGS. 1and 8 are lowered out of the way. The lift ring 39 then rises to raisethe lift pins 38 out of the pedestal 140 to a sufficient height thattheir conical heads slightly lift the wafer 142 off the robot blade. Therobot blade is then withdrawn, and the pedestal 140 and attachedcentering ring 146 are raised so that the lift pins 38 supporting thewafer 142 effectively retract toward the supporting surface 144 of thepedestal 140.

However, if the wafer 142 is not precisely centered with respect to thepedestal center 201, as it approaches the pedestal 140 it will firstencounter one or two of the centering bosses 200 on their conical tops204. The tapered surfaces of the conical tops 204 will exert sufficientlateral force on the wafer 142 that it will slide towards the center 201of the pedestal 140, thus centering the wafer 142. The wafer 142, uponbeing further lowered relative to the pedestal 140 will be located, asillustrated in the partially sectioned perspective view of FIG. 17, in acentered position inside the cylindrical bases 202 of all the centeringbosses 200.

The wafer 142 is thermally isolated from the centering ring 146 as muchas possible. Because the cylindrical bases 202 of the bosses 200 onlypartially protrude into the area of the ledge 192, a gap 206, shown inFIG. 17, is formed between the beveled edge of the wafer 142 and thestep wall 194 of the centering ring. Also, the locus of the extremeradially inward positions of the cylindrical bases 202 of the bosses 200is sized to be slightly larger than the diameter of the wafer 142, suchthat a thin gap 208 is designed to exist between the wafer edge and thecylindrical bases 202. However, because of the centering action for amisaligned wafer, the wafer 142 may contact one or two of the centeringbosses 200. Nonetheless, any resultant contact is a thin vertical linewhere the cylindrical wafer 142 contacts the cylindrical boss base 202so as to minimize conductive heat transfer.

The wafer 142 during CVD processing is gravitationally supported on thepedestal 140, but the height of the upper surface of the ledge 194 ofthe centering ring 146 is tightly controlled so that it is slightlybelow the effective supporting surface 144 of the pedestal 140 and thewafer edge is cantilevered over the upper surface of the ledge 192 witha thin gap between. The gap between the wafer edge and the ledge 192 islarge enough at the operational deposition pressures to provide goodthermal isolation, but is small enough and long enough to presentsufficient aerodynamic resistance to prevent flow of deposition gas tothe backside of the wafer. Also, the gap is thin enough to prevent aplasma from entering the gap and producing arcing.

As a result of the following structure, the centering ring 146 is notonly thermally isolated from the wafer 142 but is also thermallyisolated from the pedestal 140.

Thermal isolation of the centering ring 146 from the pedestal 140 isachieved in two ways. The centering ring is preferably composed ofaluminum or nickel-coated stainless steel. As best shown in theperspective view of FIG. 18, the centering ring 146 is supported abovethe peripheral ledge 148 of the pedestal 140 by three evenly spacedsupport pins 210 fixed into the ledge 148 of the pedestal 140 andprojecting upwardly therefrom by a precise height. The support pins 210effectively present point contacts between the pedestal 140 and thecentering ring 146 because of their very small cross sections comparedto the area of the centering ring 146. The support pins 210 arepreferably made of ceramic or a metal having a low thermal conductivity,such as stainless steel. Both the small size of the support pins 210 andtheir low thermal conductivity minimize the conduction of heat betweenthe pedestal 140 and the centering ring 146. The support pins 210loosely fit into respective radial slots 212 extending from a bottom ofan outer annular base 214 of the centering ring 146 and support thecentering ring 146 at a precisely set height above the pedestal's ledge148. The radially elongate shape of the slots 212 allows fordifferential thermal expansion between the centering ring 146 and thepedestal 140.

Radiative and convective thermal transfer between the bottom of thecentering ring 142 and the pedestal is minimized by a stack of thermallyinsulating rings 216, 218 spaced between a bottom surface of an inwardlyprojecting rim 220 of the centering ring 146 and the ledge 148 of thepedestal 140. The thermally insulating rings 216, 218 are preferablyformed of ceramic or other material of low thermal conductivity, such asstainless steel, to reduce the conductive transfer of heat therethrough.

As illustrated in the cutaway perspective view of FIG. 19, the thermallyinsulating rings 216, 218 are fixed to the bottom of the projecting rim220 of the centering ring 146 by a series of fasteners 224, such asscrews or rivets, arranged on the centering ring 146, as shown in theplan view of FIG. 14. The fasteners 224 are positioned so that gaps areformed between the pair of rings 216, 218 and both the base 214 of thecentering ring 146 and the ledge 148 of the pedestal 140. Conical heads225 of the screw fasteners 224 are recessed in counter sinks 226 at thebottom of the bottom ring 218 so as to present a smooth surface. The tworings 216, 218 are separated from each other and from the projecting rim220 of the centering ring 146 by either thermally insulating spacers 227or by spacing bumps 228, shown in FIG. 20, to form a gap 229 between therings 216, 218 as well as a gap 229A between the rings and theprojection 220 of the centering ring 146. These various gaps furthercause the rings 216, 218 to thermally float so as to more effectivelythermally separate the centering ring 146 from the pedestal 140. Twosuch rings have been shown to reduce the radiative thermal transfer by65%; three rings, by 75%.

These different thermal isolation means have been tested in a prototypereactor during normal CVD processing of the type described before. Inthese tests, the temperature of the pedestal 140 was measured to be 430°C., the temperature of the wafer 142 to be 360° C., but the temperatureof the centering ring 146 to be only 290° C. At 360° C., satisfactorythermal deposition of TiN is achieved on the wafer 142, but at 290° C.little or none of the same material deposits on the centering ring 146.These temperature differentials are driven by a showerhead 46 thatremains at about 100° C. as well as by other thermal leakages to theside.

The many means used to thermally isolate the centering ring 146 alsotend to electrically isolate it. As a result, it tends to becomeelectrically charged in the presence of a plasma in the processing space56. Such electrical charging needs to be avoided because it can producearcing between the centering ring 146 and the wafer 142, causing directdamage to the wafer. Arcing to any other point produces particles whichare apt to settle on the wafer and produce defects. Thus, it is desiredthat the centering ring 146 and the pedestal 142 be held to the sameelectrical potential.

One structure to fix the potential of the centering ring 146 to that ofpedestal 140 is a thin, solid, flexible grounding strap 230 illustratedin the cutaway perspective view of FIG. 20. The grounding strap 230 iscomposed of a thin tab 232 of an electrically conductive andmechanically soft metal, such as aluminum, which is permanently joinedto the base 214 of the centering ring 146 by a weld 234. The thicknessof the metal tab 232 is thin enough so that it conducts little heat anddoes not mechanically support the centering ring 146.

The pedestal 140 is formed on its periphery with a shallow, axiallyextending slot 236 with a deeper slot section 238 being formed at itsbottom. The tab 232 is bent at its bottom into a Z-shaped section 238such that the upper part of the tab 232 fits into the shallow slot 236and the Z-shaped section 238 fits into the deeper slot section 238. Ahole 242 formed in the very bottom of the tab 232 passes a screw 244,which is then threaded into a corresponding hole in the pedestal 140within the deeper slot section 238, thus completing the electricalgrounding. The shallow slot 236 encompasses both the tab. 232 and thehead of the screw 244 so as to maintain a nominal perimeter outline 246of the pedestal 140. Also, the shallow slot 236 and the ground strap 230are configured such that any differential motion due to temperaturedifferences between the pedestal 140 and the centering ring 146 areaccommodated without interference between the pieces while electricalcontinuity is maintained between the centering ring 146 and the pedestal140.

FIG. 21 shows a configuration according to the present invention of theRF power supply to be compared to that of FIG. 7. Here, there is nopower splitting during the plasma treatment used in conjunction with thethermal TDMAT deposition of TiN. Instead, the pedestal electrode 132 ismaintained at a ground potential, and only the upper electrode 134 ispowered by an RF generator 250 with a fixed matching circuit 252. Theliners used in the pumping channel and the grounded centering ring ofthe invention sufficiently stabilize the plasma 254 that the powersplitting between the electrodes 132, 134 as required before is nolonger necessary. It is preferred that no bias be applied to thepedestal 132 supporting the electrode since any RF bias tends toelectrically charge the wafer and to induce it to discharge to adjacentpoints, thus causing direct damage or particles.

The pumping chamber liners and the centering ring of the invention canbe easily replaced with new or refurbished components whenever films,particularly conductive films, inevitably build up on them. However,testing in a realistic operating environment has shown that even after3000 wafers, the novel design has minimized the deposition to the pointthat they do not need to be replaced. Thus, some relatively simpleimprovements to the equipment peripheral to the pedestal, all within theconfines of the existing chamber of FIG. 1, substantially reducedowntime of the CVD system while providing superior plasma conditions.

Although the invention been described with respect to a thermal CVD ofTiN followed by a plasma treatment, the invention is obviouslyapplicable to any process in which the same chamber is used for athermal metal deposition and another plasma process. For example, thetitanium layer 104 can be deposited by a plasma process using TiCl₄ asthe precursor and using the thermal TDMAT process for the TiN layer.Also, the process can be advantageously applied to CVD of conductivemetal oxides, such as perovskites including lanthanum oxide. Thecombination of deposition of conductive metals and a plasma step wouldstill present the potential problems of a thermal process depositingextraneous metal layers which could affect the plasma process. Theinvention is of course applicable to many other types of metal CVDprocesses and should be useful in dielectric CVD and other plasmaapplications as well.

While the invention has been described to specific embodiments, thoseskilled in the art will recognize that changes can be made in form anddetail without departing from the sphere and scope of the invention.

What is claimed is:
 1. A method of CVD depositing a film, comprising thesteps of: depositing a film comprising titanium nitride on a substratesupported on a top surface of a pedestal electrode within a reactionchamber in a process of thermally activated chemical vapor deposition;then applying RF power to a counter electrode while said pedestalelectrode is disposed in said chamber and is substantially grounded soas to form a plasma to treat said film; surrounding edges of saidsubstrate with a metallic ring supported on said pedestal electrode; andproviding a predetermined electrical connection from said ring to saidpedestal electrode.
 2. The method of claim 1, wherein said applying stepis performed while said reaction chamber is filled with a gas consistingessentially of argon.
 3. The method of claim 1, wherein said applyingstep is performed while said reaction chamber is filled with a gascomprising hydrogen.
 4. The method of claim 1, wherein said applyingstep is performed while said reaction chamber is filled with a gascomprising nitrogen.
 5. The method of claim 4, wherein said gasadditionally comprises hydrogen.
 6. The method of claim 1, wherein saidprocess of chemical vapor deposition includes flowingtetrakis-dimethylamido-titanium into said chamber.
 7. The method ofclaim 6, further comprising maintaining a temperature of said pedestalelectrode at a temperature of at least 360° C. during said flowing step.8. The method of claim 6, wherein said counter electrode comprises ashowerhead and wherein said flowing step flows saidtetrakis-dimethylamido-titanium through said showerhead.
 9. The methodof claim 1, further comprising: vacuum pumping said reaction chamberfrom an annular pumping channel surrounding and communicating with aprocessing space between said pedestal electrode and said counterelectrode; and placing within said annular pumping channel a pluralityof channel liners.
 10. The method of claim 1, wherein said counterelectrode comprises a showerhead and wherein said process of thermalchemical vapor deposition includes flowing a precursor gas through saidshowerhead.
 11. A method of CVD depositing a film, comprising the stepsof: depositing a film comprising an electrically conductive material ona substrate supported on a top surface of a pedestal electrode within areaction chamber in a process of chemical vapor deposition; thenapplying RF power to a counter electrode while said pedestal electrodeis substantially grounded so as to form a plasma to treat said film;surrounding edges of said substrate with a metallic ring supported onsaid top surface of said pedestal electrode; and providing apredetermined electrical connection from said ring to said pedestalelectrode.
 12. The method of claim 11, wherein said ring is entirelydisposed laterally outside of a lateral periphery of said substrate,does not shield any of a top surface of said substrate, and has a topsurface coplanar with a top surface of said substrate.
 13. A method ofCVD depositing a film, comprising the steps of: depositing a filmcomprising an electrically conductive material on a substrate supportedon a top surface of a pedestal electrode within a reaction chamber in aprocess of chemical vapor deposition; applying RF power to a counterelectrode while said pedestal electrode is substantially grounded so asto form a plasma to treat said film; surrounding edges of said substratewith a metallic ring supported on said top surface of said pedestalelectrode; thermally isolating said metallic ring from said pedestalelectrode; and providing a predetermined electrical connection from saidring to said pedestal electrode.
 14. A method of depositing a film oftitanium nitride, comprising the steps of: depositing a film comprisingtitanium nitride on a substrate supported on a pedestal electrode withina reaction chamber in a process of thermally activated chemical vapordeposition while flowing a precursor gas into said chamber; interruptingthe flowing of said precursor gas; and then performing the followingsteps of surrounding edges of said substrate with a metallic ringsupported on said pedestal electrode; providing a predeterminedelectrical connection from said ring to said pedestal electrode; andapplying RF power to a counter electrode in opposition to said pedestalelectrode in said chamber while flowing a treatment gas into saidchamber and while said pedestal electrode is substantially RF groundedso as to form a plasma of said treatment gas to treat said film.
 15. Themethod of claim 14, wherein said precursor gas comprisestetrakis-dimethylamido-titanium.
 16. The method of claim 15, whereinsaid treatment gas comprises nitrogen and hydrogen.
 17. The method ofclaim 14 wherein the thermally activated chemical vapor depositionprocess is carried out at a temperature of at least 360° C.
 18. Themethod of claim 14, wherein said counter electrode is a showerheadelectrode and wherein said precursor gas and said treatment gas areflowed through said showerhead electrode.
 19. A method of CVD depositinga film, comprising the steps of: supporting a substrate on a pedestalelectrode in a vacuum chamber; surrounding lateral sides of saidsubstrate with a metallic ring not shielding a top surface of saidsubstrate, said ring being electrically grounded to said pedestalelectrode and thermally isolated therefrom; depositing a film on saidtop surface of said substrate by a chemical vapor deposition process;and thereafter applying RF energy to a counter electrode in oppositionto said pedestal electrode to form a plasma within said vacuum chamberto plasma treat said film.
 20. The method of claim 19, wherein saidchemical vapor deposition process is thermally activated.
 21. The methodof claim 19, wherein said film comprises titanium nitride.
 22. Themethod of claim 19, wherein said plasma is formed from at least one gasselected from the group consisting of argon, hydrogen, and nitrogen.